The present invention relates to substrate processing. Specifically, the present invention relates to an apparatus and method for cleaning a processing chamber in a substrate processing system which reduces the time required to complete a dry-clean technique by increasing the flow-rate of cleaning gases therein.
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a layer, such as a metal silicide layer like tungsten silicide (WSix), on a substrate or wafer. As is well known, such a layer can be deposited by chemical vapor deposition (CVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions take place to form the desired film. In a conventional plasma-enhanced CVD (PECVD) process, a controlled plasma is formed using radio frequency (RF) energy or microwave energy to decompose and/or energize reactive species in reactant gases to produce the desired film.
One problem that arises during such CVD processes is that unwanted deposition occurs in the processing chamber and leads to potentially high maintenance costs. With CVD of a desired film on a wafer, undesired film deposition can occur on any hot surface including the heater or process kit parts of the apparatus, because the reactive gases can diffuse everywhere in the processing chamber, even within cracks and around corners. During subsequent wafer depositions, this excess growth on the heater and/or other parts of the apparatus will accelerate until a continuous metal silicide film is grown on the heater and/or these other parts. Over time, failure to clean the residue from the CVD apparatus often results in degraded, unreliable processes and defective wafers. When excess deposition starts to interfere with the CVD system's performance, the heater and other process kit parts (such as the shadow ring and gas distribution faceplate) can be removed and replaced to remove unwanted accumulations in the CVD system. Depending on which and how many parts need replacing and the frequency of the replacement, the cost of maintaining the substrate processing system can become very high.
In these CVD processes, a reactive plasma cleaning is regularly performed to remove the unwanted deposition material from the processing chamber walls, heater, and other process kit parts of the processing chamber. Commonly performed between deposition steps for every wafer or every n wafers, a reactive plasma cleaning procedure that is performed as a standard processing chamber operation where the etching gas is used to remove or etch the unwanted deposited material. One reactive plasma cleaning procedure is performed in situ in the processing chamber promotes excitation and/or disassociation of the reactant gases by the application of RF energy with capacitively coupled electrodes disposed in the processing chamber. The plasma creates a highly reactive species that reacts with and etches away the unwanted deposition material present in the processing chamber.
In addition to such in situ plasma cleaning procedures and occurring far less frequently, a second cleaning procedure involves opening the processing chamber and physically wiping the entire reactor—including the processing chamber walls, exhaust and other areas having accumulated residue—with a special cloth and cleaning liquids. This cleaning procedure is commonly referred to as a wet clean, due to the liquids employed. Failure to periodically wet clean a CVD apparatus results in accumulation of impurities that can migrate onto the wafer and cause device damage. Thus, properly cleaning a CVD apparatus is important for the smooth operation of substrate processing, improved device yield and better product performance. However, the cleaning procedures reduce the availability of a system for manufacture due to the down-time required to complete the procedures.
As an alternative to in situ plasma cleaning, a remote plasma cleaning procedure may be employed. To that end, a processing chamber is connected to a remote microwave plasma system. The remote microwave plasma cleaning procedure reduces the time required to clean the processing chamber. The high breakdown efficiency associated with a microwave plasma provides a higher etch rate (on the order of about 2 μm/min), compared to the etch rate of a capacitive RF plasma.
To further increase the etch rate of unwanted deposition materials, improved reactive plasma generators have been developed which provide an increased flow of reactive radicals into a processing chamber. One such reactive plasma generator is sold under the trademark ASTRON by Applied Science and Technology, Inc. of 35 Cabot Road, Woburn, Mass. 01801-1053. A description of the Astron is located at the following Internet address http://www.astex.com/astron.htm. The Astron is a self-contained atomic fluorine generator which uses a low-field toroidal plasma to dissociate a gas flow introduced into the plasma.
What is needed, however, is a reactive plasma cleaning procedure which further reduces the time required to clean a processing chamber, as compared to the prior art.